Digital stroke character generator

ABSTRACT

A system for generating characters by deflecting an electron beam over a screen having orthogonal X and Y axes. Beam deflection and modulation commands for each segment of each character are stored in read only memories. The deflection commands are read out to a binary rate multiplier after a character has been selected. The binary rate multiplier generates X and Y pulse trains having independently variable binary rates under the control of the deflection commands. The pulse trains are then applied to X and Y UP/DOWN counters and digital-toanalog converters to generate X and Y deflection signals in analog form having independently variable rates of change corresponding to the binary rates of the digital deflection signals. The polarity or direction of the rate of change is determined by deflection commands which control the direction of count in the UP/DOWN counters.

United States Patent [19] Chaney DIGITAL STROKE CHARACTER [451 Jan. 23,1973 1 57 ABSTRACT GENERATOR [75] Inventor: Harry Chaney, Raleigh Asystem for generating characters by deflecting an 27609 electron beamover a screen having orthogonal X and Y axes. Beam deflection andmodulation commands 3] Asslgnee: Commg Glass works commg for eachsegment of each character are stored in read only memories. Thedeflection commands are read out [22] Filed; Sept. 16, 1970 to a binaryrate multiplier after a character has been selected. The binary ratemultiplier generates X and Y [21 1 Appl' 726l3 pulse trains havingindependently variable binary rates under the control of the deflectioncommands. The [52] US. Cl. ..340/324 A, 315/18, 315/22 pulse trains arethen applied to X and Y UP/DOWN [51] Int. Cl. ..G06f 3/14 count r anddigitaLto-analog converters to generate Fleld Search 315/13, 22 X and Ydeflection signals in analog form having independently variable rates ofchange corresponding to [56] Rderences C'ted the binary rates-of thedigital deflection signals. The

UNITED STATES PATENTS polarity or direction of the rate of change isdetermined by deflection commands which control the 3,482,238 12/1969Stine ..340/324 A direction of count in the UP/DOWN counters. 3,587,0836/1971 Tubinis ..340/324 A 3,510,865 5/l970 Callahan et al ..3l5/183,334,304 8/1967 Fournier etal........ .....340/324 A Primary Examiner--Donald J. Yusko 5 Claims 4 Drawing Figures Assistant Examiner-MarshallM. Curtis Attorney-Woodcock, Washburn, I Kurtz 8g 7 Mackiewicz, ClarenceR. Patty, Jr. and Walter Zebrowski 38x 58X 6 x 74: X 76x 44x 3 1 (A- '327/ 32 32 I EEI l6 IS IS 42x8 ,363 2 f5 AND 22 OR "1 co ll en l 3 1 1 I II DEFLECTION ear 1 48x SOURCE 3 56 68x 35 I 82 1 1 i 62 l g Y 32 I 3284K g9 88 I u 4 46 gga'- 54 an 0R AND INT. CRT 36 COUNTER 4 a L PULSESHAPER 4 40 ml 2 1 502 1 T T Boy 8y 4 L m ee DEFLECTION A 32 32 32 42DATA e a L we y .7- ROM 4 2 AND 2 0R COUNTER l 1 1 K I 44y r 584 y y yDIGITAL STROKE CHARACTER GENERATOR BACKGROUND OF THE INVENTION Thisinvention relates to character generators of the stroke type.

More and more emphasis is being placed on a basic technique which may beutilized for generating characters and symbols for display regardless ofthe desired shape of these characters and symbols. The dot matrixcharacter generator wherein the electron beam intensity or Z modulationis cut on or off depending on required intensification at particulardots is the simplest way to present characters. However, this methodlimits the display to a certain type of characters. In particular, itdoes not permit the display of anything but the simplest block typecharacters and does not permit the display of script type characters.

Because of the limitation on the types of characters which may bedisplayed with a dot matrix character generator, stroke generators arein general preferred. In a stroke generator, Z modulation issubstantially continuous as the electron beam moves through a continuousstroking display in response to horizontal X axis or vertical Y axisdeflection. Although the stroke character generator is preferred inthose instances where characters other than the block type are to bedisplayed, there are difficulties associated with a stroke charactergenerator. One very significant difficulty involves the necessarycoordination between X axis and Y axis deflection where the electronbeam is being deflected in both the X axis and Y axis directionssimultaneously. If coordination between the X axis and Y axis deflectionis not maintained, it is not possible to accurately trace any characteror symbol having any segment which is non-parallel to either the X axisor the Y axis. Obviously, many characters and symbols include suchsegments.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved stroke generator for accurately displaying all charactersegments for a wide variety of characters.

In accordance with one important aspect of the invention, the charactergenerator comprises a control means having stored deflection commands. Abinary rate multiplier means generates X and Y axis pulse trains havingindependently variable binary rates under the control of the storeddeflection commands. The X and Y axis pulse trains are then converted toanalog signals having rates of change corresponding to the variablerates for deflecting an electron beam through each segment of eachcharacter during uniform segment time intervals.

In accordance with another aspect of the invention, the control meansgenerates modulation commands for Z axis modulation or electron beamintensity control.

In accordance with still another aspect of the invention, the X and Yaxis pulse trains are applied to UP/DOWN counters having a direction ofcount under the control of deflection polarity commands generated bysaid control means and then converted to analog X and Y deflectionsignals.

The foregoing and other objects, aspects, features, and advantages ofthe invention may be better un derstood from the following more detaileddescription, the appended claims and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically represents thedisplay of a character on the screen of a stroke character generatorembodying the invention;

FIG. 2 is a block diagram of a stroke character generator embodying theinvention;

FIG. 3 is a schematic diagram of particular gate means used in thestroke character generator of FIG. 2; and

FIG. 4 depicts various signals generated by the stroke charactergenerator of FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 schematically illustrates ascreen 20 of a display device such as a cathode ray tube. The screen 20,which has been subdivided into an imaginary grid for purposes ofexplaining the invention, comprises a continuum of material capable ofemitting light energy under electron bombardment from the cathode raytube electron beam source. The imaginary grid comprises a series ofequally spaced! lines parallel to the horizontal X axis and a series ofequally spaced lines parallel to the vertical Y axis. For purposes ofillustrating the invention, the letter M is shown as displayed on thescreen 20.

In order to generate the character M, the following strokes can be made.In generating a first segment 22, the electron beam is deflected alongthe Y axis from a grid position of 0, 0 to a grid position 0, 32. Thestroke of the first segment 22 is achieved by providing increasing Yaxis deflection in the form of a ramp function beginning with amagnitude of zero units and increasing to 32 units. No X deflection isapplied during this stroke.

In generating a second segment 24, the electron beam is deflected fromthe grid position 0, 32 to the grid position l3, 15 by simultaneouslyapplying chang ing X and Y deflection forces to the electron beam. In Aorder to achieve the straight line 24 connecting these positions, the Xdeflection force must increase by a magnitude of 13 units while the Ydeflection force must simultaneously decrease by a magnitude of 17units.

Third, the electron beam is stroked through a segment 26 from theposition 13, 15 to the position 25, 32 by again simultaneously applyingchanging X and Y deflection forces to the electron beam. For this thirdstroke, the X deflection force must increase by a magnitude of 12 unitswhile the Y deflection force simultaneously increases by a magnitude of17 units.

The fourth and last stroke generating a segment 28 deflects'the electronbeam from the position 25, 32 to the position 25, 0 by the applicationof a decreasing Y deflection force and a constant X deflection force.

In accordance with this invention, the deflection for generating each ofthe segments 22, 24, 26, and 28 in forming the letter M, are generatedby X axis deflection signals in the formof ramp functions having variousrates of change as well as Y axis deflection signals in the form of rampfunctions having various rates of change as shown in FIG. 4. Thesegments 24 and 26 of the character M are generated by X axis and Y axisdeflection signals in the form of ramp functions having different ratesof change asshown in FIG. 4. In order to generate segments 22 and 28 ofthe character M, ramp function Y axis deflection signals are generatedas also shown in FIG. 4 while simultaneously generating zero or constantX axis deflection signals. In order to generate the horizontal segmentsof the letter 2, it is similarly necessary to generate X axis deflectionsignals which are ramp functions while generating zero or constant Yaxis deflection signals. Finally, in order to generate the letter H, itis necessary to generate intensity control signals for modulating theelectron beam. A system embodying the invention and capable ofgenerating the foregoing deflection signals for characters such as M, Z,and H will now be described with reference to FIG. 2.

As shown in FIG. 2, the stroke character generator system comprises acontrol section 30, a pulse train generating section 32, an analogdeflection signal section 34, a modulation section 35 and a displaydevice 36. The control section 30 comprises a pair of data ROMs (readonly memories) 38X and 38Y for storing X and Y axis deflection commandsfor each segment of each character to be displayed. The memory section30 also comprises a control ROM 40 for storing additional commandsincluding Z axis modulation or beam inten sity control commands for eachsegment of each character to be displayed. In order to provide randomaccess for the particular characters selected at one of the characterselection inputs 42X and 42Y, the ROMs 38X and 38Y may comprise diodematrices where the character selection inputs 42X and 42Y are the inputlines for the diode matrices and binary deflection command outputs 44Xand 44Y, (1, 2, 4, 8, 16, 32) are the output lines of the diodematrices. Depending upon the particular characters selected at one ofthe input lines 42X, certain of the binary outputs 44X will be energizedand the resulting binary outputs will be applied to the digitaldeflection signal section 32.

The control ROM 40 having character selection inputs 46, one for eachcharacter to be selected, may also comprise diode matrices where thecharacter selection inputs 46 are the input lines and deflectionpolarity command outputs 48X and 48Y are the output lines which areconnected to the analog deflection generation section 34. A binary Zaxis modulation command output 50Z is connected to the intensity controlsection 35. The control ROM 40 also includes means for changing thedeflection and intensity control commands after each character segmentis generated. This may be accomplished by applying suitable controlsignals from the control ROM 40 to the ROMs 38X and 38Y as shown. Thecontrol function may be provided by appropriate logic circuitry wellknown in the art.

The pulse train generating section 32 comprises a source of clock pulseswhich may be gated by the control ROM 40 through a connection not shownand a BRM (binary rate multiplier) 53 comprising a ripple counter 54, apulse shaper 56, AND gate means 58X and 58Y and OR gate means 60X and60Y. As the clock pulses from the source 52 enter the ripple counter 54having a four bit section 62 and a two bit section 64, a plurality ofpulse trains are generated at each of the pulse train outputs 66. Thepulse rates of each of the pulse trains correspond to the binary outputs44X and 44Y (1, 2, 4, 8, 16, 32), i.e., of one pulse per unit of time,two pulses per unit of time etc. Each of the pulses of the pulse trainis then applied to the pulse shaper 56 before application to the ANDmeans 58X and 58Y at inputs 68X and 68Y.

As shown in FIG. 3, each of the AND gate means 58X and 58Y comprises agroup of six AND gates 70, one for each of the pulse trains from theripple counter 54. By selectively enabling particular AND gates inresponse to deflection commands from the ROMs 38X and 38Y, particularpulse trains will be passed by the AND gate means 58X and 58Y and the ORgate means 60X and 60Y. Where more than one AND gate 70 is enabled, morethan one pulse train will be passed and the pulse trains leaving the ORgate means 60X and 60Y will be composite pulse trains having pulse ratesequal to the sum of the rates of the component pulse trains.

The analog deflection signal section comprises the UP/DOWN counters 74Xand 74Y in series with digital-to-analog convertors 76X and 76Yrespectively. As the pulse trains from the OR gate means 60X and 60Yenter the UP/DOWN counters 74X and 74Y respectively, binary outputs ofthe UP/DOWN counters produce a count representing the pulse rate of thecomposite pulse trains. Note that pulse rate is a direct function ofparticular deflection commands at the output 44X and 44Y which are thenapplied to the AND gate means 58X and 58Y. Since the deflection commandsat the outputs 44X and 44Y are mutually and independently variabledepending upon the particular segment of a particular character, thebinary rate of the composite pulse trains applied to the UP/DOWNcounters 74X and 74Y are mutually and independently variable. Of course,the resulting analog deflection signal generated by thedigital-to-analog convertor 76X and 76Y are ramp functions havingmutually independent rates of change corresponding to the binary rates.Accordingly, the analog deflection signals which are applied todeflection circuitry 80X and 80Y associated with a cathode ray tube 82of the display section 36 are mutually independent.

The composite pulse trains from the OR gate means 60X and 60( are alsoapplied to the intensity control section 35 comprising an OR gate 84 inseries with an AND gate 86 selectively enabled by the intensity controlcommands at the modulation command output 50Z of the control ROM 40. Theresulting digital intensity control signal is then applied to intensitycontrol circuitry 88 of the display section 36.

The operation of the stroke character generator of FIG. 2 will now bedescribed by describing the generation of the character M as shown inFIG. 1. With the character M selected at the character selection inputs42X, 42Y, and 46, the ROM outputs 44X, 44Y, 48X, 48Y, and 50Z are asfollows:

44X 48X 50Z 48Y 44Y 32168421 32168421 0000000 11 100000 0011011 10010001 0011001 11 010001 0000000 10 100000 During the stroking of thesegment 22, the outputs 44X are all in the low state 0 while the output44Y (32) is in the high state l so as to enable the AND gate 70 of theAND gate means 58Y having a pulse train input of 32 pulses per unit oftime as shown in FIG. 4. By placing the UP/DOWN counter 74Y in the upcounting state by a 1 at the output 48Y and modulating the beam with anoutput of 1" at the output 50Z, the ramp function for stroking thesegment 22 is generated as shown in FIG. 4.

At the end of this stroke, the control ROM 40 changes the commands fromthe control section 30. In particular, the outputs 44X (8, 4, and l) arenow I with the outputs 44Y (16 and l) l to stroke the segment 24. As aresult, the AND gates 70 of the AND gate means 58X which are coupled topulse trains having 8, 4, and l pulses per unit of time and the ANDgates 70 of the AND gate means 58Y which are coupled to pulse trainshaving a pulse rate of 16 and 1 pulses per unit of time are applied tothe UP/DOWN counters 74X and 74Y. Because of the OR gate 60X and 60Y,composite pulse trains comprising 13 pulses per unit of time and 17pulses per unit of time as shown in FIG. 4 are applied respectively toUP/DOWN counters 74X and 74Y. The UP/DOWN counter 74X is maintained inthe up counting state since the output 48X is I while the UP/DOWNcounter 74Y is in the down counting state since the output 48Y is 0 togenerate the ramp functions shown in FIG. 4. The electron beam ismodulated throughout the stroking of the segment 24 since the output 50Zis 1 The stroking of the segment 26 is similar to the stroking of thesegment 24 except that the outputs 44X (8 and 4) are l to produce only12 pulses per unit of time as shown in FIG. 4 for application to theUP/DOWN counters 74X. In addition, the UP/DOWN counter 74Y is now in anup counting state due to the 1 at the output 48Y.

The stroking of the segment 28 is substantially identi cal to thesegment 22 except that the UP/DOWN counter 74Y is in the down countingstate due to the 0" at the output 48Y and the count of the UP/DOWNcounter 74X remains at 25 since all outputs 44X are iKOQQ Although theletters M, Z, and H are specifically mentioned in the foregoing, itshould be appreciated that character generator of FIG. 2 may be utilizedto generate a wide variety of characters including the ASCII businesscharacters. It should also be understood that the various'componentsshown in block form comprise commercially available and otherwisesubstantially conventional elements well known to those of ordinaryskill in the art.

Although the invention has been described in terms of a particularembodiment, various changes and modifications may be made withoutdeparting from the spirit of the invention or the scope of the appendedclaims.

What is claimed:

1. A character generator system of the type having a display deviceincluding a screen, an electron beam source, an X deflection means fordeflecting the beam across the screen in a direction parallel to the Xaxis, and a Y deflection means for deflecting the beam across the screenin a direction parallel to the Y axis, said system comprising:

a control means for generating digital X axis deflection commandsrepresenting appropriate X axis deflection and digital Y axis deflectioncommands representing appropriate Y axis deflection during timeintervals of substantially uniform length for each segment of eachcharacter to be displayed;

a pulse train generating means comprising a source of pulses and abinary rate multiplier coupled to the output of said control means forgenerating digital X axis and Y axis pulse trains for each segmenthaving independently variable binary rates determined by said X axis andY axis deflection commands, said X axis and Y axis pulse trains for eachsegment being generated in one of said time intervals of substantiallyuniform length regardless of segment length;

an analog deflection signal generating means coupled to the output ofsaid pulse train generating means for generating analog X axis and Yaxis deflection signals from said X axis and Y axis pulse trainsrespectively for application to the X deflection means and the Ydeflection means respectively, said analog X axis and Y axis deflectionsignals generating each segment of each character during one of saidtime intervals of substantially uniform length, said analog signalshaving rates of change corresponding to said independently variablebinary rates; and

an intensity control gating means having an input coupled to the outputof said. binary rate multiplier and an output coupled to said displaydevice for controlling the intensity of said electron beam in responseto said X axis and Y axis pulse trains.

2. The character generator system of claim 1 wherein said control meansincludes means for generating Z axis modulation commands for eachsegment of each character to be displayed for selectively enabling theintensity control gating means in response to said Z axis modulatingcommands.

3. The character generator system of claim 2 wherein said control meansgenerates polarity commands for each segment of each character to bedisplayed, and said analog deflection signal generating means includesmeans for controlling the polarity of said rate of change of said analogX axis and Y axis deflection signals in response to said polaritycommands.

4. The character generator system of claim 1 wherein said binary ratemultiplier comprises:

a counter generating a plurality of outputs having different binaryrates;

AND gate means comprising an X group of gates and a Y group of gates,the plurality of said outputs from said counter being applied tocorresponding inputs of said X group of gates and said Y group of gates,said X group of gates and said Y group of gates being selectivelyenabled by said deflection commands so as to generate a combined outputat said X group of gates and a combined output at said Y group of gateshaving binary rates equal to the sum of the binary rates for theparticular gates enabled in said X group of gates and said Y group ofgates respectively; and

an X OR gate means and a Y OR gate means having inputs coupled to theoutputs of said X group of gates and said Y group of gates respectively,the outputs of said X OR gate means and said Y OR gate means providingthe inputs to said X analog deflection signal means and said Y analogdeflection signal means respectively.

5. The character generator system of claim 4 wherein said control meansgenerates deflection polarity commands for each segment of eachcharacter to be displayed, said analog deflection signal generatingmeans comprising X and Y axis UP/DOWN counters coupled to the output ofsaid X OR gate means and said Y OR gate means respectively and furthercomprising X and Y axis digital-to-analog convertors coupled to theoutputs of said X and Y axis UP/DOWN counters, the counting direction ofeach said UP/DOWN counter being controlled by said deflection polaritycommands.

1. A character generator system of the type having a display deviceincluding a screen, an electron beam source, an X deflection means fordeflecting the beam across the screen in a direction parallel to the Xaxis, and a Y deflection means for deflecting the beam across the screenin a direction parallel to the Y axis, said system comprising: a controlmeans for generating digital X axis deflection commands representingappropriate X axis deflection and digital Y axis deflection commandsrepresenting appropriate Y axis deflection during time intervals ofsubstantially uniform length for each segment of each character to bedisplayed; a pulse train generating means comprising a source of pulsesand a binary rate multiplier coupled to the output of said control meansfor generating digital X axis and Y axis pulse trains for each segmenthaving independently variable binary rates determined by said X axis andY axis deflection commands, said X axis and Y axis pulse trains for eachsegment being generated in one of said time intervals of substantiallyuniform length regardless of segment length; an analog deflection signalgenerating means coupled to the output of said pulse train generatingmeans for generating analog X axis and Y axis deflection signals fromsaid X axis and Y axis pulse trains respectively for application to theX deflection means and the Y deflection means respectively, said analogX axis and Y axis deflection signals generating each segment of eachcharacter during one of said time intervals of substantially uniformlength, said analog signals having rates of change corresponding to saidindependently variable binary rates; and an intensity control gatingmeans having an input coupled to the output of said binary ratemultiplier and an output coupled to said display device for controlLingthe intensity of said electron beam in response to said X axis and Yaxis pulse trains.
 2. The character generator system of claim 1 whereinsaid control means includes means for generating Z axis modulationcommands for each segment of each character to be displayed forselectively enabling the intensity control gating means in response tosaid Z axis modulating commands.
 3. The character generator system ofclaim 2 wherein said control means generates polarity commands for eachsegment of each character to be displayed, and said analog deflectionsignal generating means includes means for controlling the polarity ofsaid rate of change of said analog X axis and Y axis deflection signalsin response to said polarity commands.
 4. The character generator systemof claim 1 wherein said binary rate multiplier comprises: a countergenerating a plurality of outputs having different binary rates; ANDgate means comprising an X group of gates and a Y group of gates, theplurality of said outputs from said counter being applied tocorresponding inputs of said X group of gates and said Y group of gates,said X group of gates and said Y group of gates being selectivelyenabled by said deflection commands so as to generate a combined outputat said X group of gates and a combined output at said Y group of gateshaving binary rates equal to the sum of the binary rates for theparticular gates enabled in said X group of gates and said Y group ofgates respectively; and an X OR gate means and a Y OR gate means havinginputs coupled to the outputs of said X group of gates and said Y groupof gates respectively, the outputs of said X OR gate means and said Y ORgate means providing the inputs to said X analog deflection signal meansand said Y analog deflection signal means respectively.
 5. The charactergenerator system of claim 4 wherein said control means generatesdeflection polarity commands for each segment of each character to bedisplayed, said analog deflection signal generating means comprising Xand Y axis UP/DOWN counters coupled to the output of said X OR gatemeans and said Y OR gate means respectively and further comprising X andY axis digital-to-analog convertors coupled to the outputs of said X andY axis UP/DOWN counters, the counting direction of each said UP/DOWNcounter being controlled by said deflection polarity commands.